The efficiency of a screw jack is maximum, when (where α = Helix angle, and φ = Angle of friction)
α = 45° + φ/2
α = 45° - φ/2
α = 90° + φ
α = 90° - φ
Correct Answer :
B. α = 45° - φ/2
Related Questions
The relation l = (2/3).(j + 2) apply only to kinematic chains in which lower pairs are used. This may be used to kinematic chains in which higher pairs are used, but each higher pair may be taken as equivalent to
One lower pair and two additional links
Two lower pairs and one additional link
Two lower pairs and two additional links
Any one of these
A pantograph is a mechanism with
Lower pairs
Higher pairs
Rolling pairs
Turning pairs
In a four-bar chain it is required to give an oscillatory motion to the follower for a continuous rotation of the crank. For the lengths of 50 mm of crank and 70 mm of the follower, determine theoretical maximum length of coupler. The distance between fixed pivots of crank and followers is
95 mm
Slightly less than 95 mm
Slightly more than 95 mm
45 mm
The static balancing is satisfactory for low speed rotors but with increasing speeds, dynamic balancing becomes necessary. This is because, the
Unbalanced couples are caused only at higher speeds
Unbalanced forces are not dangerous at higher speeds
Effects of unbalances are proportional to the square of the speed
Effects of unbalances are directly proportional to the speed
The example of spherical pair is
Bolt and nut
Lead screw of a lathe
Ball and socket joint
Ball bearing and roller bearing
The brake commonly used in railway trains is
Shoe brake
Band brake
Band and block brake
Internal expanding brake
In a system subjected to damped forced vibrations, the ratio of maximum displacement to the static deflection is known as
Critical damping ratio
Damping factor
Logarithmic decrement
Magnification factor
In a steam engine, the earlier cut-off with a simple slide valve may be obtained by increasing the steam lap and the angle of advance of the eccentric but keeping constant the travel and lead of the valve, this method will
Cause withdrawing or throttling of steam
Reduce length of effective stroke of piston
Reduce maximum opening of port to steam
All of these
The balancing of a rigid rotor can be achieved by appropriately placing balancing masses in
A single plane
Two planes
Three planes
Four planes
A spring controlled governor is said to be unstable when the controlling force
Increases as the radius of rotation decreases
Increases as the radius of rotation increases
Decreases as the radius of rotation increases
Remains constant for all radii of rotation
3.The retardation of a flat faced follower when it has contact at the apex of the nose of a circular arc cam, is given by (where OQ = Distance between the centre of circular flank and centre of nose)
ω² × OQ
ω² × OQ sinθ
ω² × OQ cosθ
ω² × OQ tanθ
If some links are connected such that motion between them can take place in more than one direction, it is called
Incompletely constrained motion
Partially constrained motion
Completely constrained motion
Successfully constrained motion
If the number of links in a mechanism is equal to l, then the numbers of possible inversions are equal to
l - 2
l - 1
l
l + 1
The centre of gravity of a coupler link in a four bar mechanism will experience
No acceleration
Only linear acceleration
Only angular acceleration
Both linear and angular acceleration
Coriolis component is encountered in
Quick return mechanism of shaper
Four bar chain mechanism
Slider crank mechanism
Both (A) and (C) above
The included angle for the V-belt is usually
10° to 20°
20° to 30°
30° to 40°
60° to 80°
In its simplest form, a cam mechanism consists of following number of links
1
2
3
4
Minimum number of teeth for involute rack and pinion arrangement for pressure angle of 20° is
18
20
30
34
Idler pulley is used
For changing the direction of motion of the belt
For applying tension
For increasing velocity ratio
All of the above
Two pulleys of radii r₁ and r₂ and at distance x apart are connected by means of an open belt drive. The length of the belt is
π (r₁ + r₂) + (r₁ + r₂)²/x + 2x
π (r₁ + r₂) + (r₁ - r₂)²/x + 2x
π (r₁ - r₂) + (r₁ - r₂)²/x + 2x
π (r₁ - r₂) + (r₁ + r₂)²/x + 2x
Relationship between the number of links (L) and number of pairs (P) is
P = 2L - 4
P = 2L + 4
P = 2L + 2
P = 2L - 2
The maximum efficiency of a screw jack is
(1 - sinφ)/(1 + sinφ)
(1 + sinφ)/(1 - sinφ)
(1 - tanφ)/(1 + tanφ)
(1 + tanφ)/(1 - tanφ)
The driving and driven shafts connected by a Hooke's joint will have equal speeds, if
cosθ = sinα
sinθ = ± tanα
tanθ = ± cosα
cotθ = cosα
If the pressure angle is __________, a reciprocating follower will jam in its bearings.
Small
Too small
Large
Too large
The Ackermann steering mechanism is preferred to the Davis type in automobiles because
The former is mathematically accurate
The former is having turning pair
The former is most economical
The former is most rigid
When the primary direct crank of a reciprocating engine makes an angle of θ with the line of stroke, then the secondary direct crank will make an angle of _________ with the line of stroke.
θ/2
θ
2θ
4θ
The indicator using Watt mechanism is known as
Thompson indicator
Richard indicator
Simplex indicator
Thomson indicator
A spring controlled governor is found unstable. It can be made stable by
Increasing the spring stiffness
Decreasing the spring stiffness
Increasing the ball mass
Decreasing the ball mass
In S.H.M., the velocity vector w.r.t. displacement vector
Leads by 90°
Lags by 90°
Leads by 180°
Are in phase
Which of the following is a turning pair?
Piston and cylinder of a reciprocating steam engine
Shaft with collars at both ends fitted into a circular hole
Lead screw of a lathe with nut
Ball and a socket joint